The wireless LAN has attracted considerable attention as a system that relieves users from the troublesome wiring of the wired LAN. The wireless LAN can eliminate most of wired cables in a workspace such as an office, which makes it possible to move personal computers and other communication terminals comparably easily. In recent years, accompanied with the enhanced speed and reduced price of the wireless LAN, the demand for it is remarkably increased. Especially recently, the personal area network (PAN) is under the examination for introduction, so that people can communicate information with a small-scale wireless network using multiple electronic devices surrounding people. As an example, different wireless communication systems and wireless communication devices are stipulated, which use the frequency bandwidths that do not require a license by the supervising agency, such as 2.4 GHz band and 5 GHz band.
Recently, a wireless communication system using an ultra wide bandwidth covering 3 GHz to 10 GHz, which is called the ‘ultra wide band (UWB) communication’ has drawn considerable attention as a wireless communication system that realizes a short-distance ultra-high speed transmission; and the practical development thereof is expected. At present, the data transmission system with a packet structure including the preamble is being designed as an access control system for the UWB communication in IEEE 820.15.3 and so forth.
Now, building up a wireless network in a room will make the multi-path environments, in which the receiving devices receive a direct wave having multiple reflected waves and delayed waves overlapped. The multi-path environments will cause delay distortion (or frequency selective fading), which effects errors on the communication. And, the inter-symbol interferences due to the delay distortion will be generated.
One of the main countermeasures for the delay distortion is the multi-carrier transmission system. Since the multi-carrier transmission system distributes transmitted data to plural carriers of different frequencies, the bandwidths of the carriers each become narrow, which makes it difficult to receive the influences of the frequency selective fading.
In the OFDM (Orthogonal Frequency Division Multiplexing) system being one of the multi-carrier transmission systems, the frequencies of the carriers each are set in a manner that the carriers each are mutually orthogonal in the symbol interval. During transmission of information, the system performs serial/parallel conversion to the information transmitted in serial at each symbol cycle that is slower than the data transmission rate, allocates the plural data converted into the serial/parallel format to the carriers each, performs the amplitude and phase modulation to the carriers each, performs inverse FFT to the plural carriers, and thereby converts the carriers on the frequency axis into the signals on the time base while retaining the orthogonality on the frequency axis to transmit the information. During reception, the system performs the operation reverse to the above; that is, it performs FFT to convert the signals on the time base into the signals on the frequency axis, performs the demodulations corresponding to the respective modulation systems to the carriers each, performs parallel/serial conversion to the demodulated signals, and reproduces the original information transmitted in the serial format.
The OFDM modulation system is adopted as the standard for the wireless LAN, for example, in IEEE 802.11a/g. Also in IEEE 802.15.3a, the standardization of the UWB communication system adopting the OFDM modulation system (hereunder, called ‘OFDM_UWB’) is in progress, in addition to the DS-UWB system with the diffusion speed of DS information signal raised to the limit, and the impulse-UWB system for transmitting and receiving the information signal that uses the impulse signal string having a very short cycle of about some 100 pico-seconds. In case of the OFDM_UWB communication system, the OFDM modulation is under examination, which performs frequency hopping (FH) on three sub-bands whose bandwidths are 528 MHz each in the frequency band covering 3.14 to 4.8 GHz, and uses IFFT/FFT having each frequency band composed of 128 points (see Non-patent Document 1).